[syzbot] [net?] general protection fault in __ip6_del_rt_siblings

[syzbot <syzbot+a73e5ee0fd534fed75bd@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    89a312991dc6 Merge tag 'cifs-fixes-7.3-rc2' of https://git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14096f79580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b454dc6b1b7acd30
dashboard link: https://syzkaller.appspot.com/bug?extid=a73e5ee0fd534fed75bd
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/120fc5c06ced/disk-89a31299.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/accc50a0c85b/vmlinux-89a31299.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0aec83a14f94/bzImage-89a31299.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a73e5ee0fd534fed75bd@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000004: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
CPU: 0 UID: 0 PID: 15348 Comm: syz.1.2507 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:__ip6_del_rt_siblings+0x31e/0x7c0 net/ipv6/route.c:4056
Code: f7 4d 8d 74 24 10 4c 89 f0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 f7 e8 80 fb 2d f8 4d 8b 36 49 83 c6 20 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 63 fb 2d f8 49 8b 06 4c 39 e0 74
RSP: 0018:ffffc9000564f120 EFLAGS: 00010202
RAX: 0000000000000004 RBX: ffffc9000564f430 RCX: 0000000000080000
RDX: ffffc90005222000 RSI: 0000000000000307 RDI: 0000000000000308
RBP: 1ffff110069ec605 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed100c66d413 R12: ffff888034f63000
R13: dffffc0000000000 R14: 0000000000000020 R15: ffffc9000564f4b8
FS:  00007fd3d4c866c0(0000) GS:ffff888125bd5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb3e2f95ff8 CR3: 0000000060a36000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ip6_route_del+0x1054/0x1110 net/ipv6/route.c:4232
 inet6_rtm_delroute+0x5d7/0x6d0 net/ipv6/route.c:5669
 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7132
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7f5/0x990 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 ____sys_sendmsg+0x565/0x870 net/socket.c:2713
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767
 __sys_sendmsg net/socket.c:2799 [inline]
 __do_sys_sendmsg net/socket.c:2804 [inline]
 __se_sys_sendmsg net/socket.c:2802 [inline]
 __x64_sys_sendmsg+0x1b7/0x290 net/socket.c:2802
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd3d6a2e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd3d4c86028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fd3d6cb5fa0 RCX: 00007fd3d6a2e159
RDX: 0000000000000000 RSI: 0000200000000280 RDI: 0000000000000004
RBP: 00007fd3d6ac5024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd3d6cb6038 R14: 00007fd3d6cb5fa0 R15: 00007fff66fa0ad8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__ip6_del_rt_siblings+0x31e/0x7c0 net/ipv6/route.c:4056
Code: f7 4d 8d 74 24 10 4c 89 f0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 f7 e8 80 fb 2d f8 4d 8b 36 49 83 c6 20 4c 89 f0 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 f7 e8 63 fb 2d f8 49 8b 06 4c 39 e0 74
RSP: 0018:ffffc9000564f120 EFLAGS: 00010202
RAX: 0000000000000004 RBX: ffffc9000564f430 RCX: 0000000000080000
RDX: ffffc90005222000 RSI: 0000000000000307 RDI: 0000000000000308
RBP: 1ffff110069ec605 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed100c66d413 R12: ffff888034f63000
R13: dffffc0000000000 R14: 0000000000000020 R15: ffffc9000564f4b8
FS:  00007fd3d4c866c0(0000) GS:ffff888125bd5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa5bde16d58 CR3: 0000000060a36000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	f7 4d 8d 74 24 10 4c 	testl  $0x4c102474,-0x73(%rbp)
   7:	89 f0                	mov    %esi,%eax
   9:	48 c1 e8 03          	shr    $0x3,%rax
   d:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
  12:	74 08                	je     0x1c
  14:	4c 89 f7             	mov    %r14,%rdi
  17:	e8 80 fb 2d f8       	call   0xf82dfb9c
  1c:	4d 8b 36             	mov    (%r14),%r14
  1f:	49 83 c6 20          	add    $0x20,%r14
  23:	4c 89 f0             	mov    %r14,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	4c 89 f7             	mov    %r14,%rdi
  34:	e8 63 fb 2d f8       	call   0xf82dfb9c
  39:	49 8b 06             	mov    (%r14),%rax
  3c:	4c 39 e0             	cmp    %r12,%rax
  3f:	74                   	.byte 0x74


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